The Neurobehavioral Core will provide scientific leadership in the characterization of neuropsychological (NP) deficits and their functional impact in HIV infected persons. Specifically, we will: (1) interact with our HNRC colleagues to identify critical questions in neuroAIDS that can be examined using neurobehavioral outcomes; (2) characterize longitudinally the NP status (and functional correlates) of large samples of HIV+ and HIV- subjects, (3) help develop transdisciplinary research that links neuropsychology to other approaches; (4) develop innovations in neurobehavioral research relevant to neuroAIDS; (5) provide technical assistance and consultation on state-of-the-art neurobehavioral assessment; (6) support preliminary studies that require neurobehavioral data; (7) provide mentorship for students, fellows, and junior faculty in theory and techniques of neuropsychology; and (8) collaborate with the HNRC Coordinating Core to help disseminate neurobehavioral information as it applies to neuroAIDS. NP data will be used as clinical correlates for existing and new studies examining effects of HIV infection on the brain. Examples of collaborations with other HNRC cores and their investigators include studies of NP correlates of HIV viral load and excitotoxic substances in the CSF; association of white matter changes in the brain with deficit in specific cognitive domains; and relationship of antemortem NP status to postmortem neuropathologic measures of brain viral burden and synaptodendritic complexity. In addition, NP and functional skills information will serve as outcome measures in clinical trials, including their impact on treatment adherence. The Neurobehavioral Core will implement a number of innovative techniques and will address scientific questions that are of interest not only in the area of neuroAIDS but which also will serve more generally to advance the measurement of NP impairment and its consequences. These include (1) establishing norms for detecting significant change in NP performance over repeated measurements; (2) continuing to develop appropriate normative data for under-served (minority) populations; (3) developing more efficient NP testing approaches that are most sensitive to deficits typically observed in people infected with HIV (alone or in conjunction with drug addiction); (4) examining the relationship between NP status and adherence to treatment regimens; and (5) exploring the role of fluctuating NP impairment on everyday functioning and survival.